External mix air assisted spray nozzle assembly

ABSTRACT

A spray device comprising a body having a liquid discharge passage and a spray nozzle assembly affixed to the body is provided. The spray nozzle assembly includes a liquid spray tip for directing liquid from the liquid passage in the body into a predetermined spray pattern and an atomizing fluid cap. The liquid spray tip includes a forwardly extending nose portion that defines a liquid discharge orifice. The nose extends through a central opening in the air cap thereby defining an annular atomizing fluid discharge orifice that communicates with an atomizing fluid inlet. The nose extends in a downstream direction past the central opening in the air cap such that the liquid discharge orifice is arranged at least approximately 2 mm. downstream of the annular atomizing fluid discharge orifice.

FIELD OF THE INVENTON

The present invention relates generally to spray nozzle assemblies, andmore particularly, to external mix air atomizing spray nozzle assembliesin which a discharging liquid flow stream is atomized and formed intothe desired spray pattern by pressurized air externally of the liquiddischarge orifice.

BACKGROUND OF THE INVENTION

External mix air atomizing spray nozzles are known for their ability tocontrol liquid particle size and spray distribution by pressurized air,independent of liquid flow rate. They also can be used with relativelylow pressure air supplies which can be generated by inexpensive blowers,rather than air compressors. Because atomization occurs externally ofthe liquid discharge orifice, the intermixing liquid and air streams canbe susceptible to control and performance problems.

Conventional external mix spray nozzle assemblies, such as depicted inFIGS. 1 and 2, commonly comprise a nozzle body or spray tip 25 a havinga forwardly extending nose 31 a that defines a liquid discharge orifice32 a and an air cap 26 a mounted in surrounding relation to the nozzlebody 25 a. The air cap 26 a has a central opening 33 a within which thenozzle body nose 31 a is positioned for defining a central annularatomizing air passage 34 a about the nose 31 a for dischargingpressurized air in surrounding relation to the liquid flow stream forpreliminarily atomizing and axially directing the discharging liquidstream. The air cap 26 a further has a pair of integrally formed,diametrically opposed ears 50 which define fan air discharge orifices 39a for directing pressurized air streams at an angle, such as 45°, to thedischarging liquid for further breaking down the liquid and directingthe liquid particles into the desired spray pattern.

In the conventional air cap 26 a the ears 50 from which the angled airjets are directed protrude from a front face of the air cap and extendaxially downstream of the liquid discharge orifice 32 a. While this formof air cap performs well with many materials, in spraying materials thatare prone to build up, the protruding ears can be problem prone. Liquidforcefully atomized downstream of the liquid discharge orifice can causerandom spray to collect on the ears and on the face of the air cap,resulting in a build up that eventually interferes with performance ofthe nozzle.

In the conventional external mix spray nozzle assembly, the liquiddischarge orifice defining nose 31 a also generally is flush with thecentral air cap end portion through which the central opening 33 aextends, not extending outwardly more than one millimeter beyond thecentral air cap opening 33. This arrangement can further cause build upof solid material onto the exposed surfaces of the air cap. Indeed,liquid particles drawn radially outwardly by a low pressure area createdby the atomizing air discharging from the central annular air passagesabout the nose can cause overspray to be deposited onto the face of theair cap surrounding the central annular air passage. This build up alsocan eventually interfere with the spray nozzle performance, and in somecases, block the atomizing air completely.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an external mix airatomizing spray nozzle assembly which is adapted for more efficient andreliable operation.

Another object is to provide an external mix air atomizing spray nozzleassembly as characterized above which is operable with less likelihoodof spray material build up on the face of the air cap or in and aroundthe pressurized air discharge orifices.

A further object is to provide a spray nozzle assembly of the above kindthat is relatively simple in design and lends itself to economicalmanufacture.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of an external mix air atomizing spraynozzle assembly typical of the prior art;

FIG. 2 is an enlarged fragmentary section of the spray tip and air cap,showing the central liquid and pressurized air discharge orifices of theprior art nozzle assembly shown in FIG. 1;

FIG. 3 is a longitudinal section of an illustrative spray device havingan spray nozzle assembly in accordance with the present invention;

FIG. 4 is a downstream end view of the spray nozzle assembly of thespray device shown in FIG. 3;

FIGS. 5 and 6 are fragmentary sections of the illustrated spray nozzleassembly, taken in the planes of line 5-5 and 66, respectively, in FIG.4; and

FIG. 7 is an enlarged fragmentary section of the central end portion ofthe spray nozzle assembly as depicted in FIG. 6, again taken in theplane of line 6-6 in FIG. 4.

While the invention is susceptible of various modifications andalternative constructions, a certain illustrative embodiment thereof hasbeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to FIG. 3 of the drawings, there isshown an illustrative air atomizing liquid spray device 10 comprising aspray gun body 11 having an external mix air assisted spray nozzleassembly 12 in accordance with the invention at a downstream end. Thespray device 10 in this instance has a reciprocatable valve needle 13for controlling discharging liquid spray for the nozzle assembly 12. Thebasic structure and mode of operation of the spray device are known inthe art, for example, as shown in the aforementioned U.S. Pat. No.5,707,010 and U.S. application Ser. No. 09/892,138, the disclosures ofwhich are incorporated herein by reference. The overall structure andmode of operation of the spray device should be understood to beillustrative of only one example of a spray device with which the nozzleassembly of the present invention may be used.

The illustrated spray gun body 11 axially supports the valve shut-offneedle 14 within an axial liquid flow passage 13 and has a liquid inletport 15 for connection to the supply liquid to be sprayed and apressurized air inlet port 18 for connection toga pressurized air sourceor other pressurized fluid for assisting in atomization of the liquid tobe sprayed and for effecting controlled axial movement of the valveneedle 14 between on and off positions.

For operating the valve needle 14, a rear end of the body 11 carries adrive piston assembly 18 and a compression spring 19 which is confinedbetween an outer side of the piston assembly 18 and an internal end wallof a cap 20 screwed on to the rear of the body 11. The compressionspring 19 biases the piston assembly 18, and hence the valve needle 14affixed thereto forwardly to a fully seated, i.e. valve “closed”position as depicted in FIG. 3. The valve needle 14 is moved axially inthe opposite direction (to the right as viewed in FIG. 3) against theforce of spring 19 by control drive air or other fluid supplied to theinlet port 1 and through one or more connecting ports into a cylinderchamber 21 adjacent a forward side of the moveable piston assembly 18.The supply of control fluid, e.g. compressed air, is controlledexternally, such as by solenoid actuated valves, for controlled openingof the valve needle 14 to allow liquid to be discharged through thespray nozzle assembly 12. It will be appreciated from the foregoing thatthe valve needle 14 may be selectively operated between on and offpositions, including operation in a high speed cyclic on-off mode, e.g.as rapid as 180 on-off cycles per minute.

The spray nozzle assembly 12, as depicted in FIGS. 3-7, comprises anozzle body 25 in the form of a liquid spray tip and an air cap 26mounted in surrounding relation to the discharge end of the nozzle body25 by a retaining ring 28. The nozzle body 25 is affixed to the forwardend of the spray gun body 11 by a threaded stem 29 and has a centralaxial liquid passageway 30 communicating with the housing liquidpassageway 13. The nozzle body 25 in this case has a forwardly extendingnose portion 31 which defines a liquid discharge orifice 32 and whichextends axially into a central opening 33 of the air cap 26, as depictedin FIGS. 5 and 7. The nose portion 31 is slightly smaller in diameterthan the central air cap opening 33 for defining an annular atomizingair discharge orifice 34 communicating with the pressurized air inletport 18 through an annular chamber 35 for discharging atomizing airparallel to liquid discharging from the liquid discharge orifice 32. Theair cap 26 further is formed with a pair of opposed fan air passages 39communicating with an annular manifold or air chamber 38, which in turncommunicates with the pressurized air inlet port 18 for atomizing,forming, and directing the discharging liquid into the desired spraypattern. The fan air passages 39 in this case are oriented at an angleof about 45° to the longitudinal axis of the spray nozzle assembly.While in the illustrated spray device a single air source may be usedfor both atomizing air and fan air, it will be appreciated that separateair sources may be utilized for greater control.

In accordance with an important aspect of the invention, the liquiddischarge orifice defining nose of the spray tip or nozzle body extendsoutwardly beyond the central end face of the air cap a distance of atleast 2 mm. such that the annular atomizing air discharge orifice 34 issufficiently upstream of a liquid discharge orifice 32 to be moreeffectively protected from the build up of solid material in liquidbeing atomized downstream of the liquid discharge orifice. In theillustrated embodiment, the central air cap portion through which thecentral opening 33 extends is defined by a substantially rectangular endface section 40 located between opposite rearwardly slanted sidesurfaces 41 of the air cap 26. The spray tip nose 31 extends at least 2mm. beyond the central end face section 40, and preferably, a distanceof 1 mm. plus the diameter of the liquid discharge orifice. Hence, ifthe liquid discharge orifice is 1 mm. the spray tip nose 31 preferablyextends a distance of at least 2 mm. beyond the central air cap end face40 and if the liquid discharge orifice is 2 mm. the nose 31 preferablyextends a distance of at least 3 mm. beyond the central air cap end face40. Such arrangement results in the liquid discharge orifice 32 beinglocated sufficiently downstream the annular air atomizing dischargeorifice 34 for minimizing the undesirable build up of solid materialsabout the annular air atomizing discharge orifice which might otherwiseadversely affect the spray performance. At the same time, it has beenfurther found that a low pressure condition resulting from the flow ofpressurized atomizing air through the annular orifice 34 effectivelydraws the discharging liquid radially outwardly for interaction with andatomization by the discharging annular atomizing air stream.

In further carrying out the invention, the discharge orifices of theangled fan air passages 39 also are located in recessed, upstreamrelation to the liquid discharge orifice such that liquid drawn radiallyoutwardly by the low pressure area about the atomizing air dischargeorifice and broken up by the atomizing air again does not substantiallyimpact the end face of the air cap or cause undesirable build up ofsolid materials about either the atomizing and fan air dischargeorifices 34, 39. In the illustrated embodiment, the end face 44 of theair cap defined between the tapered side surfaces 41 extends insubstantial co-planar relation vertically across the end of the air cap,as viewed in FIG. 4. The end face 40 is formed with a pair of V-shapedcut-outs 42 on opposite sides of the central air cap opening 33, witheach V-shaped cut-out 42 having an outer surface oriented 45° to thelongitudinal axis through which a respective angled fan passage 39communicates. The other side of each V-shaped cut-out 42 defines anangled ramp surface which facilitates direction of the fan air radiallyinwardly toward the liquid discharging from the liquid discharge orifice32. With the fan air discharge orifices 39 being formed through theangled sides of the V-shaped cuts 42, they are located both rearwardlyof the liquid discharge orifice 32 as well as the atomizing air orifice34 so as to be substantially protected from exposure to randomlydirected liquid particles. With the fan air discharge orifices 39recessed in such manner, it also can be seen that the air cap need nothave forwardly projecting ears typical of the prior art.

From the foregoing, it can be seen that while the illustrated spraynozzle assembly atomizes and forms the liquid spray pattern away fromthe end face of the air cap, the likelihood of sprayed material buildingup on the face of the air cap and around the air atomizing and fan airdischarge orifices is substantially reduced. This is accomplished by aspray nozzle assembly which has an earless air cap design and a spraytip with an extended liquid discharge orifice defining nose.

1. A spray device comprising: a body having a liquid discharge passage;a spray nozzle assembly affixed to the body, the spray nozzle assemblyincluding a liquid spray tip for directing liquid from the liquidpassage in the body into a predetermined spray pattern and an atomizingfluid cap, the liquid spray tip including a forwardly extending noseportion that defines a liquid discharge orifice, the nose extendingthrough a central opening in the air cap thereby defining an annularatomizing fluid discharge orifice that communicates with an atomizingfluid inlet, the nose extending in a downstream direction past thecentral opening in the air cap such that the liquid discharge orifice isarranged at least approximately 2 mm. downstream of the annularatomizing fluid discharge orifice.
 2. The spray device according toclaim 1 wherein the atomizing fluid cap includes a pair of opposedangled fan atomizing fluid passages each having a respective fandischarge orifice that is located upstream of the annular atomizingfluid discharge orifice and the liquid discharge orifice.
 3. The spraydevice according to claim 2 wherein the atomizing fluid cap includes anend face having a pair of V-shaped cutouts therein on opposite sides ofthe atomizing fluid discharge orifice, each fan discharge orifice beingarranged in an angled side of a respective one of the V-shaped cutoutsso as to direct atomizing fluid towards the fluid discharging from thefluid discharge orifice.
 4. The spray device according to claim 1wherein the liquid discharge orifice is located downstream of theannular atomizing fluid discharge orifice a distance of at leastapproximately 1 mm. plus the diameter of the liquid discharge orifice.5. The spray device according to claim 1 further including a valveneedle supported in the body for movement between a retracted openposition for permitting liquid discharge through the liquid spray tipand a closed position for preventing liquid discharge through the liquidspray tip.
 6. A spray device comprising: a body having a liquiddischarge passage; a spray nozzle assembly affixed to the body, thespray nozzle assembly including a liquid spray tip for directing liquidfrom the liquid passage in the body into a predetermined spray patternand an atomizing fluid cap, the liquid spray tip including a forwardlyextending nose portion that defines a liquid discharge orifice, the noseextending through a central opening in the air cap thereby defining anannular atomizing fluid discharge orifice that communicates with anatomizing fluid inlet, the atomizing fluid cap including a pair ofopposed angled fan atomizing fluid passages each having a respective fandischarge orifice that is located upstream of the annular atomizingfluid discharge orifice and the liquid discharge orifice.
 7. The spraydevice according to claim 6 wherein the atomizing fluid cap includes anend face having a pair of V-shaped cutouts therein on opposite sides ofthe atomizing fluid discharge orifice, each fan discharge orifice beingarranged in an angled side of a respective one of the V-shaped cutoutsso as to direct atomizing fluid towards the fluid discharging from thefluid discharge orifice.
 8. The spray device according to claim 6further including a valve needle supported in the body for movementbetween a retracted open position for permitting liquid dischargethrough the liquid spray tip and a closed position for preventing liquiddischarge through the liquid spray tip.
 9. A spray device comprising: abody having a liquid discharge passage; a spray nozzle assembly affixedto the body, the spray nozzle assembly including a liquid spray tip fordirecting liquid from the liquid passage in the body into apredetermined spray pattern and an atomizing fluid cap, the liquid spraytip including a forwardly extending nose portion that defines a liquiddischarge orifice, the nose extending through a central opening in theair cap thereby defining an annular atomizing fluid discharge orificethat communicates with an atomizing fluid inlet, the nose extending in adownstream direction past the central opening in the air cap such thatthe liquid discharge orifice is arranged a distance of at leastapproximately 1 mm. plus the diameter of the liquid discharge orificedownstream of the annular atomizing fluid discharge orifice, theatomizing fluid cap including a pair of opposed angled fan atomizingfluid passages each having a respective fan discharge orifice that islocated upstream of the annular atomizing fluid discharge orifice andthe liquid discharge orifice.
 10. The spray device according to claim 9further including a valve needle supported in the body for movementbetween a retracted open position for permitting liquid dischargethrough the liquid spray tip and a closed position for preventing liquiddischarge through the liquid spray tip.